One phrase that I always remember from The Great Gatsby is “yellow cocktail music”, a term that uses the language of synesthesia to convey the feeling of drunkenness.  With a similarly passionate attitude, Van Campen’s The Hidden Sense is a fascinating attempt to make sense of this most poetic of brain conditions.

First, it’s important to get the definition of synesthesia straight.  This is “a neurological phenomenon that occurs when a stimulus in one sense modality immediately evokes a sensation in another sense modality” (1).  Synesthesia is most well-known in the form termed ‘word-colour synesthesia’, where a person sees a particular colour when they read a particular word or number.  This is only the most common form, though: van Campen reports an astonishing 43 types of synesthesia that have been reported, including smells → colours; tastes → colours; personalities → colours; emotions → smells: orgasm → colours; time units → colours; vision → temperatures; and sounds → smells, to name a few (131).

One of the most interesting aspects of the condition is its social dimension.  ‘Sufferers’ (which is probably the wrong word, since the condition sounds quite exciting) are usually unaware that other people don’t experience the world the same way that they do.  Many stories describe a person’s realisation that another family member is a synesthete:

When I was twenty, I came back from college on the semester break and my whole family – mother, brother, father and I – were sitting around the dinner table, and for some strange reason I don’t understand, I said “the number five is yellow”, and my father said “No, it’s yellow ochre”.  And my mother and brother looked at each other like this is a game but they don’t know the rules. (36)

Many synesthetes have less positive experiences – there are several stories about children who suppressed knowledge of their abilities after being ridiculed by classmates for being ‘weird’.  To counter the isolation often felt by synesthetes, van Campen takes pains to show that synesthesia is not a ‘delusion’.  In brain scans conducted on word-colour synesthetes, for example, the part of the brain responsible for the perception of colour lights up when the patient reads a word, suggesting that there is a direct neural connection that causes the condition (5).

The book includes many visual representations of synesthetic patients’ own representations of numbers and words, which are extremely helpful in understanding how such experiences are represented in the mind.  The variation between different people’s representations is striking, and van Campen’s willingness to provide space for different patients’ visual perceptions is one of the book’s strongest points.  Browsing through the colour plate section, where you can see (for example) a diagram of differently-coloured decades, goes a long way towards revealing just how unique and nuanced these experiences are.

Most interestingly, van Campen advances the theory that we are all born synesthetes, but most of us unlearn this ability at the age of about six months.  This is because the separate sense channels are not formed at birth, and it takes up to a year for them to separate.  Until that time, babies experience the world in a single, unified sense, a state that has much in common with synaesthesia.

Another of van Campen’s challenges to our standard way of thinking about the senses is his claim that we have many more than five – we just don’t have names for most of them.  Quoting the Dutch physician Albert Soesman, Van Campen puts forward the idea that we have “additional senses, including a sense of self-movement, a sense of equilibrium, a sense of temperature, a sense of speech, a sense of imagination, a sense of life, and a sense of the self” (100).  Ultimately, the author notes, “senses are arbitrary divisions”, and we have many more than we realise (100).  When looked at in this way, the condition of ‘synaesthesia’ can be seen as a symptom of our reductive tendency to assign a small and arbitrary complement of senses to ourselves.  It’s a provocative thought.

Incredibly, babies aged six months can transfer information between the senses far more efficiently than slightly older children can.  For instance, the researcher Daphne Maurer conducted the following experiment:

Suppose you darken a room and give a newborn a ball in the dark, let it feel it for a moment, and then turn on the light.  When you show the ball and a cube to the newborn at a distance, the newborn will look at the ball instead of the cube…Somehow, the newborn is able to perceive the resemblance between the tactile impression and the visual impression. (32)

Children lose this ability, though, at the age of about six months, and must painstakingly learn it again by repeated attempts to transfer information between the senses – a process that takes them another six months.  This leads to the conclusion that “everyone is probably born as a synesthete” (32).

While the chapters dealing with patients’ direct experiences and experimental data are quite profound, those trying to approach the issue through the writings of famous artists are less rewarding.  Looking at Vladimir Nabokov, Vincent van Gogh, and other famous synesthetes, van Campen tries to draw conclusions about synesthesia and artistic ability that don’t always seem plausible.  This includes studies of the effects of hallucinogenic drugs, using the writings of people such as de Quincy and Baudelaire.  While this is interesting, it suffers in comparison to the quite stunning hard data presented in other chapters, and does not significantly advance the author’s findings.  

Van Campen has succeeding in writing a book that has quite literally changed the way that I think about the world.  His careful exploration of the condition of synesthesia –  incidentally, he is a synesthete – unearths a new and strange world of experience that most people cannot access.  By taking the time to explain the complexities of the condition in all of its different manifestations, The Hidden Sense offers a tantalising glimpse into a previously inaccessible world of experience. 


The Hidden Sense: Synesthesia in Art and Science
(2008)

by Cretien van Campen
ISBN: 9780262220811
MIT Press (distributed in Australia by Footprint Books)
185pp AUD$58.95